Post launch inert gas production and utilization system and method

ABSTRACT

A gas production and utilization system includes an ionic liquid having an electrochemical window and engineered to produce a specific gas. A power supply is configured to apply a voltage potential across electrodes disposed in the ionic liquid at a level higher than the electrochemical window of the ionic liquid to decompose the ionic liquid. The resultant gas is delivered to a pressure vessel and may be utilized in a variety of different ways.

GOVERNMENT RIGHTS

This invention was made with U.S. Government support under Contract No.FA9300-10-C-2101 awarded by AFRL/Edwards AFB. The Government may havecertain rights in the invention

FIELD OF THE INVENTION

This application pertains to spacecraft gas production, utilization, andstorage.

BACKGROUND OF THE INVENTION

In space applications, a liquid propellant may be delivered underpressure to a thruster using a gas expulsion tank containing a gas underpressure. See, for example, U.S. Pat. No. 5,471,833 incorporated hereinby this reference.

Such gas expulsion tanks can be heavy, occupy significant real estate,and can impose hazards to a launch since it can be dangerous to storeand/or transport gasses at high pressures. If the propellant ispressurized before and during launch and leaks, the result can also bedisastrous. Using a mechanical pump system to pressurize the propellantpost launch requires power and can be prone to various failure modes.

Certain gasses can be generated post-launch, but energy (e.g., heat) isusually required and such gas generation techniques can be dangerousonboard a spacecraft. Also, some gasses, for example oxygen, can begenerated by electrolysis. But, other dangerous gasses such as hydrogenin excess, for example, are also generated. Also, it is desirable thatonly inert gasses be used for certain subsystems such as for propellantpressurization. Moreover, the gas used for propellant pressurizationmust be at a sufficiently high pressure, for example 350 psi.

Ionic liquids (salt with a low melting temperature, for example moltensalts composed of anions and cations with a melting point below about100° C.) have been used as electrolytes in batteries, for example.Typically, any gas production by electrolysis of an ionic liquid used asan electrolyte is undesirable and is to be avoided.

Finally, U.S. Pat. No. 7,563,308, incorporated herein by this referenceproposes using ionic liquids to store various gases. See also U.S. Pat.No. 7,297,289 incorporated herein by this reference.

SUMMARY OF THE INVENTION

Provided in various aspects of the invention is an innovativepost-launch propellant pressurization subsystem which is shelf storable,easily scalable, and contains few moving parts as a safe and low costalternative to prior systems. The system is easily scalable toaccommodate propulsion systems of various types and sizes without thesafety concern of filled high-pressure gas tanks.

The subject invention, however, in other embodiments, need not achieveall these objectives and the claims hereof should not be limited tostructures or methods capable of achieving these objectives.

Featured is a post-launch inert gas production method. An ionic liquidis engineered to produce a given inert gas, e.g., CO₂. The ionic liquidis decomposed by electrolysis to produce the inert gas at a givenpressure. The pressurized inert gas can then be utilized in a variety ofways.

In preferred examples, the ionic liquid has an electrochemical windowand electrolysis includes applying a voltage potential across the ionicliquid at a voltage above the electrochemical window of the ionicliquid. Preferably, the ionic liquid resides in a housing with at leastfirst and second electrodes therein connected to a power supply. In onepreferred design, the power supply is configured to provide AC power tothe electrodes at a voltage of 6-16 volts.

The interior of the housing may include an electrically insulativematerial. Also, there can be a plurality of electrodes in an array. Thehousing is typically coupled to an outlet conduit. A filter allows theinert gas produced to exit the housing via the outlet while retainingthe ionic liquid in the housing. In one example, the filter includes aporous frit material.

Utilizing the pressurized gas may include delivering the pressured gasto a pressure vessel. In one design, the pressure vessel includes apropellant therein delivered to a thruster. In another example,utilization of the pressurized gas includes delivering the pressurizedgas directly to a cold-gas thruster.

Also featured is a post-launch inert gas production method comprisingdecomposing an ionic liquid by electrolysis to produce a pressurizedinert gas by applying a voltage potential to the ionic liquid at avoltage above the electrochemical window of the ionic liquid andutilizing said pressurized inert gas by delivering the pressurized inertgas to a pressure vessel.

One gas production and utilization system includes a housing includingspaced electrodes therein, an ionic liquid in the housing, a powersupply configured to apply a voltage potential across said electrodes ata level sufficient to decompose the ionic liquid and produce apressurized gas, and a pressure vessel for storing the pressurized gasso produced.

In one design, a gas production and utilization system comprises ahousing including spaced electrodes therein, an ionic liquid in thehousing having an electrochemical window and engineered to produce aspecific gas, a power supply configured to apply a voltage potentialacross said electrodes at a level higher than the electrochemical windowof the ionic liquid to decompose the ionic liquid and produce thespecific gas under pressure, and a pressure vessel for the pressurizedgas.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Other objects, features, and advantages will occur to those skilled inthe art from the following description of a preferred embodiment and theaccompanying drawings, in which:

FIG. 1 is a schematic view of a prior art propellant pressurizationsystem;

FIG. 2 is a schematic diagram showing several of the primary componentsassociated with a post launch gas production and utilization system inaccordance with the invention; and

FIG. 3 is a schematic view showing another example of an electrolysismodule in accordance with the invention.

DETAILED DESCRIPTION OF THE INVENTION

Aside from the preferred embodiment or embodiments disclosed below, thisinvention is capable of other embodiments and of being practiced orbeing carried out in various ways. Thus, it is to be understood that theinvention is not limited in its application to the details ofconstruction and the arrangements of components set forth in thefollowing description or illustrated in the drawings. If only oneembodiment is described herein, the claims hereof are not to be limitedto that embodiment. Moreover, the claims hereof are not to be readrestrictively unless there is clear and convincing evidence manifestinga certain exclusion, restriction, or disclaimer.

FIG. 1 shows a source 10 of propellant 12 delivered to thruster 14 viagas expulsion tank 16 containing pressurized gas 18 delivered topropellant 12 via valve 19. Such a system results in a heavy, fairlylarge tank 16. This source of pressurized gas can be dangerous duringlaunch of a space craft employing thruster 14. In other prior artdesigns the propellant is pressurized and similar inherent dangersexist.

In one example of the invention, housing 20 (e.g., stainless steel)includes spaced electrodes 22 a and 22 b therein connected to powersupply 24 configured to apply a voltage of, for example, 6-16 volts (at,for example, 0.1 amps) to electrodes 22 a and 22 b. An ionic liquid suchas 2-hydroxyethylammonium formate (2-HEAF) (an equimolar mixture offormic acid and 2-hydroxyethylamine) is used in housing or module 20.Other possible ionic liquids include 1-Ethyl-3-methylimidazoliumbis(trifluoromethylsulfonyl)imide (EMI-TFSI) or1-Ethyl-3-methylimidazolium tetrafluoroborate (EMI-BF4). Compared toEMI-TFSI and EMI-BF4, the 2-HEAF ionic liquid has a much narrowerelectrochemical window (e.g., 0.1-1.1V). Preferably, the ionic saltchosen fills the interior of housing 20 and has an electrochemicalwindow typically in the range of 0-5 volts. Electrochemical windowtypically refers to the potential difference between oxidation potential(anodic limit) and the reduction potential (cathodic limit). Anelectrochemical window may be defined as the voltage range between whicha substance is neither oxidized nor reduced.

Post launch, by applying a voltage potential at a voltage level abovethe electrochemical window of the ionic liquid, the ionic liquiddecomposes (e.g., 2-HEAF) at least in the area proximate the electrodes22 a, 22 b and produces a pressurized inert gas (e.g., mainly CO₂) whichcan be utilized, for example, by delivering the pressurized inert gas topressure vessel 30 shown in this particular example with bladder 32 (ora piston) used to pressurize propellant 34 on the other side of bladder32 to be delivered to and used in thruster 36. Controller 40 (e.g., amicrocontroller, or the like) can be employed to operate power source 24and valve 42 in the conduit 44 between housing 20 and pressure vessel 30based on the pressure inside housing 20 as measured by pressure sensor42. In other examples, the gas produced is delivered to a separatepressure vessel and then, for example, to a propellant vessel.

The result is a low cost, lightweight, small inert gas production systemwhich produces pressurized gas with very little power input. An AC powersupply is preferred to prevent degradation of electrodes 22 a and 22 b.In one example, a small housing 20 containing just 20 cc of ionic liquidwhich produced a gas sufficient to pressurize 280 cc of propellant to350 psi for 30 minutes of operation of thruster 36.

The interior 50 of housing 20 may include (e.g., a coating of) anelectrically insulative material such as a ceramic. Filter 52 (e.g.,made of a porous frit material such as stainless steel or titanium) maybe disposed at outlet 52 to trap the ionic liquid in housing 20 butallow the pressurized gas produced by electrolysis to exit.

In FIG. 3, ionic liquid 26 in module 20′ is maintained in contact withan array of electrodes 22 connected to power supply 24 by using springloaded plate 60. A power supply which provides an alternating currentvoltage is preferably used. Spring 62 a and 62 b urge plate 60 downwardin the figure and keep the ionic liquid dispersed about the electrodesin low or zero gravity operations. Other mechanisms for maintaining theionic liquid about the electrodes may be used and the electrodes may bedesigned to attract the ionic liquid thereto by surface tension for lowgravity operations. Also, in this particular example, the gas producedby the decomposition of the ionic liquid is supplied directly to coldgas thruster 70 by valve 72.

When the ionic liquid 2-HEAF was tested after electrolysis, a gaseousmixture composed primarily of CO₂ was produced. As the 2-HEAF ionicliquid decomposes, the gas is pressurized and can be utilized by avariety of different types of subsystems.

Because the pressurized gas is generated in-situ, the system can bestored and launched unpressurized as opposed to previous systems wheretanks of high pressure gas were required to be stored and launched. Thisnew system is low cost because there are few moving parts which alsoreduces the likelihood of failure. The preferred gasses generated arerelatively non-toxic, do not react with the fuel/oxidizer, and arestable which reduces the potential risk of a rupture or other failureoccurs during use or testing. The power supply can be operated a variouspower levels depending on the required pressurization rate and availableelectrical power. Tests have demonstrated that a minimum input power of0.5-1 W reaches a gas pressurization of 300 psig. Tests havedemonstrated that a minimum input power of 0.5-1 W produces over 200standard CCs of gas from only 4 mL of ionic liquid.

In another test, the ionic liquid EMI-IM was used in an 11 ml stainlesssteel test cell housing with opposing 1.6 mm diameter platinum rods.Utilizing the ionic liquid 2-HEAP, however, resulted in a gas productionon the order of magnitude greater than when the EMI-IM ionic liquid wasused. Thus, the ionic liquid chosen in the preferred embodiment ispreferably engineered to maximize gas production for a given powerconsumption. Another benefit of 2-HEAF is that it decomposes intorelatively safe, inert substances. The composition of the product gaswas confirmed to be 90% CO₂ and 10% CO and possibly a fraction ofhydrogen.

The pressurization process can begin as soon as power is available tothe system, typically when the spacecraft solar array is deployed. Thereaction can be stopped and restarted at any time in order to divertpower to other systems as needed. Because the product gasses arenon-corrosive, no exotic materials are needed and typically commercialoff the shelf valves and sensors can be utilized.

By purposely decomposing an ionic liquid via AC electrolysis in reactionhousing 20, FIG. 2, the product gas or gasses can be utilized in variousapplications which require a pressurized gas. Preferably, the gasses aregenerated for utilization in situations where space for storing gas islimited or where it is dangerous to transport or store gasses at highpressures. The specific ionic liquid chosen should decompose to gas fromliquid in high fractions to minimize the volume and mass of the ionicliquid required. Furthermore, toxicity, condensation temperatures ofgasses produced, and neutrality of the gasses may be important factorsin choosing the appropriate ionic liquid. An ionic liquid which does notthermally decompose may be favored. The electrodes may exist in an arrayas shown. In one test a ⅛″ electrode, gap was used for 1-2 cc of theionic liquid. Use of an AC voltage prevents electrode fouling. In a testwhere the produced gas was used in a cold gas thruster, electrolysis wasperformed on 4 cc of the 2-HEAF ionic liquid at 16 volts AC at 60 Hzusing a 0.060″ electrode gap. Gas was generated at a pressure ofapproximately 180 psia. A valve was opened and the working gas wasdelivered to non-pressurized tubing reducing the pressure to 120 psia.The average thrust measured was 124.4 mN for a duration of 0.75 seconds.Using the ionic liquid 2-HEAF, the best gas production rate was achievedat 16 volts at 10 Hz. Testing with electrode gaps of 0.030, 0.060, and0.090″ demonstrated the gas generation rates increased with greaterelectrode gaps and gaps generation efficiency remains relativelyconsistent despite changes in gap size. During one test, 204 sec gas wasgenerated from 4 cc of 2-HEAF ionic liquid during 294 hours ofelectrolysis with a consistent gas generation efficiency averaging 0.43scc/kJ. This amount of gas would be sufficient to pressurize a 10 ccvessel to 300 psig. The ionic liquid 2-HEAF was tested and appears to belargely compatible with platinum, aluminum, macor ceramic, and Teflon.The gas generation rate of 7.5 sec/hr and a maximum gas generationefficiency of 5 scc/kJ was noted.

In the electrolysis process of the 2-HEAF ionic liquid, the ethanolammonium cation will first adsorb on the electrode and then be reducedto ethanolamine and hydrogen. The format anion will also first adsorb onthe electrode and then be oxidized to form CO2 and protons. For thepresent application, the 2-HEAF ionic liquid is a good candidate becauseof the carboxylate anion which will preferably generate CO2 gas. Inaddition, this particular ionic liquid also has a relative short alkylchain in the cation which can prevent the formation of excess gaseoushydrocarbon. Other ionic liquids can be chosen for use based on the sameor similar criteria.

Utilization of the gas produced by the electrolysis method may furtherinclude using the gas in pneumatic actuators (valves, cylinders, and thelike), pneumatic motors, compressors, cold-gas thrusters, and otherexamples such as tire inflation systems and insect traps (if CO₂ is theproduced gas). Typically, the gas is used for a broad range ofthrusters, mono- and bi-propellant rockets, electric propulsion andcold-gas thrusters, and the like.

Although specific features of the invention are shown in some drawingsand not in others, this is for convenience only as each feature may becombined with any or all of the other features in accordance with theinvention. The words “including”, “comprising”, “having”, and “with” asused herein are to be interpreted broadly and comprehensively and arenot limited to any physical interconnection. Moreover, any embodimentsdisclosed in the subject application are not to be taken as the onlypossible embodiments.

In addition, any amendment presented during the prosecution of thepatent application for this patent is not a disclaimer of any claimelement presented in the application as filed: those skilled in the artcannot reasonably be expected to draft a claim that would literallyencompass all possible equivalents, many equivalents will beunforeseeable at the time of the amendment and are beyond a fairinterpretation of what is to be surrendered (if anything), the rationaleunderlying the amendment may bear no more than a tangential relation tomany equivalents, and/or there are many other reasons the applicant cannot be expected to describe certain insubstantial substitutes for anyclaim element amended.

Other embodiments will occur to those skilled in the art and are withinthe following claims.

1. A post-launch inert gas production method comprising: choosing anionic liquid engineered to produce a given inert gas; decomposing theionic liquid by electrolysis to produce the inert gas at a givenpressure; and utilizing said pressurized inert gas.
 2. The method ofclaim 1 in which the ionic liquid is engineered to produce CO₂.
 3. Themethod of claim 1 in which the ionic liquid has an electrochemicalwindow and electrolysis includes applying a voltage potential across theionic liquid at a voltage above the electrochemical window of the ionicliquid.
 4. The method of claim 3 in which the ionic liquid resides in ahousing with at least first and second electrodes therein connected to apower supply.
 5. The method of claim 4 in which the power supply isconfigured to provide AC power to said electrodes.
 6. The method ofclaim 5 in which AC power is provided to said electrodes at a voltage of6-16 volts.
 7. The method of claim 4 in which the interior of thehousing includes an electrically insulative material.
 8. The method ofclaim 4 in which there are a plurality of electrodes in an array.
 9. Themethod of claim 4 in which the housing is coupled to an outlet conduit.10. The method of claim 9 further including a filter allowing the inertgas produced to exit the housing via the outlet while retaining theionic liquid in the housing.
 11. The method of claim 10 in which thefilter includes a porous frit material.
 12. The method of claim 1 inwhich utilizing the pressurized gas includes delivering the pressuredgas to a pressure vessel.
 13. The method of claim 12 in which thepressure vessel includes a propellant therein delivered to a thruster.14. The method of claim 1 in which utilization of the pressurized gasincludes delivering the pressurized gas to a cold-gas thruster.
 15. Apost-launch inert gas production method comprising: decomposing an ionicliquid by electrolysis to produce a pressurized inert gas by applying avoltage potential to the ionic liquid at a voltage above theelectrochemical window of the ionic liquid; and utilizing saidpressurized inert gas by delivering the pressurized inert gas to apressure vessel.
 16. A gas production and utilization system comprising:a housing including spaced electrodes therein; an ionic liquid in thehousing; a power supply configured to apply a voltage potential acrosssaid electrodes at a level sufficient to decompose the ionic liquid andproduce a pressurized gas; and a pressure vessel for storing saidpressurized gas.
 17. The system of claim 16 in which the ionic liquid isengineered to produce CO₂.
 18. The system of claim 16 in which the ionicliquid has an electrochemical window and the power supply is configuredto apply a voltage potential across said electrodes at a voltage abovethe electrochemical window of the ionic liquid.
 19. The system of claim16 in which the power supply is configured to provide AC power to saidelectrodes.
 20. The system of claim 19 in which the power supply isconfigured to provide AC power at a voltage of 6-16 volts to saidelectrodes.
 21. The system of claim 16 in which the interior of thehousing includes an electrically insulative material.
 22. The system ofclaim 16 in which there are a plurality of electrodes in an arraydisposed within the housing.
 23. The system of claim 16 in which thehousing includes an exit filter allowing the inert gas produced to exitthe housing while retaining the ionic liquid in the housing.
 24. Thesystem of claim 23 in which the filter includes a porous frit material.25. The system of claim 16 in which the pressure vessel includes apropellant therein pressurized by the pressurized gas.
 26. A gasproduction and utilization system comprising: a housing including spacedelectrodes therein; an ionic liquid in the housing having anelectrochemical window and engineered to produce a specific gas; a powersupply configured to apply a voltage potential across said electrodes ata level higher than the electrochemical window of the ionic liquid todecompose the ionic liquid and produce said specific gas under pressure;and a pressure vessel for said pressurized gas.